| The following historical excerpts are
taken from the book From the Ground Up: The Autobiography
of an Aeronautical Engineer, by Fred E. Weick and James
R. Hansen, Smithsonian Institution Press, Copyright 1988.
Not long after work on the ERCO airplane was under way
in 1937, the author, Fred Weick was asked by Henry Berliner
to visit Europe to learn as much as possible about the
design of a new type of wooden propeller that was being
manufactured by the Schwarz Company in Germany and by
Airscrews Ltd. In England.
ERCO had sold many of its machine tools for the construction
of aircraft to most of the major European countries,
but in Russia and Germany the company could not receive
payment that could be transferred into Amercan dollars,
instead, it had to make some sort of barter arrangement.
From Germany, it got the right to make Schwarz propellers,
which were being manufactured in large quantities not
only by Schwarz but also by Airscrews Ltd in England.
The Schwarz blade consisted essentially of a main core
of laminated spruce or other light wood, which merged
into a root of impregnated and compressed hardwood known
as “compreg”. The compreg root was threaded
and screwed into a steel ferule that supported the blade
in the hub. The remainder of the blade was covered completely
with a heavy coating of reinforced cellulose acetate
sheet, whose leading edge was armored with a flush strip
of metal. Thus, the wooden core was well protected against
contact with pebbles, winders, sand, rain, hail, seawater
and so on. These propellers are described in detail in
a paper entitles “Composite Wood and Plastic Propellers
Blades” by Fred E. Weick that was printed in the
SAE journal in June 1939 . The main advantage of the
Schwarz propellers lay in their light weight, as compared
with the large aluminum-alloy propellers which at that
time were being used with the most powerful reciprocating
engines.
Up to 1936 ERCO had never been involved per se in building
airplanes, but its products had consisted entirely of
machines for making airplanes. These machines included
propeller-profiling machines, sheet-metal flanging machines
and stretch presses and the automatic punching and riveting
machines invented by Lee Marchant.
Soon after Mr Weick’s return to ERCO and finishing
his report, ERCO got the Schwarz-type propeller activity
under way. As time went on, ERCO made quite a fair number
of large propellers of this type, mostly for experimental
airplanes, because the props were light and could be
designed and manufactured quickly, requiring no special
tooling. Hollow steel propellers soon dominated this
market, though. The only real quantity production of
propeller blades at ERCO occurred during World War II
when they manufactured quite a number of all-compreg
blades for adjustable-pitch propellers used on planes
like the Stinson L-5 Grasshopper reconnaissance plane.
By January 1941, nearly a year before the United States
entered World War II, manufacturers could get no more
aluminum-alloy sheet or even aluminum-alloy extrusions
for use in small commercial airplanes. The nation’s
entire production of these items was being used for military
purposes, either to build up our own forces or to help
those who would later be our allies.
Erco’s main production during the war was in machine-gun
turrets. They continued the production of propellers,
but the output consisted mainly of all-compreg blades.
T.O. No. 03-20F-2.
*ERCO* Engineering and Research Corporation
Riverdale, Maryland, USA
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